1. Field of the Invention
The present invention relates to a process for the preparation of polyether-ester polyols. More particularly, the invention relates to the preparation of these polyols by reacting a polyoxyalkylene polyether polyol, a cyclic anhydride and 5 percent or less ethylene oxide.
2. Description of the Prior Art
The preparation of polyether-ester polyols by the reaction of an alkylene oxide with a half acid ester obtained by the reaction of a polyol with an unsaturated acid anhydride is well known in the art as taught in U.S. Pat. Nos. 3,931,092, 4,014,846, 4,093,573 and 4,144,395. These patents relate to uncatalyzed or trialkylaminecatalyzed reactions. U.S. Pat. No. 3,374,208 teaches the use of various metal catalysts for the preparation of polyesters. The prior art, however, does not teach the preparation of polyether-ester polyols having a primary hydroxyl content of greater than 50 percent and 5 percent or less ethylene oxide.